JPS60142718A - Electronic ac voltage variable device - Google Patents

Abstract

PURPOSE:To simplify the system constitution by using an induction motor of an air-conditioner as a load of a voltage variable device and mounting a power MOSFET of the voltage variable device to the enclosure of the motor so as to save a heat sink. CONSTITUTION:One terminal of the AC input of a diode bridge 11 of an electronic AC voltage variable device is connected to a single phase AC power source 1 via a load 4 together with the other AC input terminal. Furthermore, a drain and a cathode of the power MOSFET12 are connected to the DC output terminal of the bridge 11 and a series circuit comprising a fixed resistor 9 and a variable resistor 10 is connected in parallel between the drain and the cathode. Then a gate of the FET12 is connected to a connecting point of the resistors 9, 10 and a voltage applied to the load 4 is changed by changing the resistance value of the resistor 10. The induction motor 13 of the air-conditioner is used as the load 4, and the FET12 is mounted on the enclosure of the induction motor 13 so as to save the heat sink thereby simplifying the system constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to a relatively light-loaded power supply connected to an AC power supply.
- It performs voltage control and is mainly suitable for speed control of induction motors in air conditioners.

Conventional configuration and its problems A conventional example will be explained using FIGS. 1 to 3.

FIG. 1 shows a generally widely known variable output voltage type autotransformer (hereinafter referred to as a slideac).

1 is AC power supply, 2 is Slydac, 3 is Slydac 2
output tap, 4 is the load. The power supply WEE v of the AC power supply 1 applied to the input of the switching slide duck 2 is proportionally reduced depending on the position of the output tap 3 and is applied to the load 4 as a load voltage vL.

The state of the power supply voltage ``I'' and the charge voltage ``L'' is shown in FIG. 3 by rough solid lines and broken lines, respectively.

The method of varying the AC output voltage using SLIDAC 2 has a simple structure and is relatively inexpensive, so it is widely used, but its disadvantages are that it is heavy and has a mechanical structure, making it unsuitable for control as a system. It can be said that Furthermore, since the factor that determines the output voltage is mechanical contact, there is also the problem of low long-term reliability and low environmental reliability.

Next, FIG. 2 shows an example of an electronic alternating voltage variable system.

5.6 is a diode, 7 is an N P N transistor, 8
is a PNP l-transistor, 9 is a fixed resistor, and 10 is a variable resistor. 1 and 4 are the same as in FIG.

The base voltages of the NPN transistor 7 and the PNP transistor 8 are determined by the fixed resistor 9 and the variable resistor 10, the emitter potential is determined, and therefore the voltage applied to the load 4 is determined. Each transistor 7.8 corresponds to the positive phase and negative phase of the AC power source 1, and the AC power source 1 and
The difference from the voltage applied to the load 4, ie, the voltage drop, is consumed as vcE of the transistors 7 and 8. Diodes 5 and 6 are necessary to block base-to-collector current when the respective transistor 7.8 is reverse biased.

The circuit shown in Figure 2 also allows the power supply voltage VI and load voltage vL to be
The voltage waveform of is shown in FIG.

According to the AC voltage variable system using transistors in Figure 2, the load voltage ■L can be varied by varying 10 variable resistors, but transistors 7 and 8, which mainly consume power, become two elements. However, there are limits to miniaturization and cost reduction due to the necessity of insulating the collectors from each other. In addition, the load voltage vL is always applied to both ends of the variable resistor 1o included in the base of the transistor 7.8, and as a result, the variable resistor 1o needs to have a withstand voltage equivalent to the voltage of the AC power supply 1. Furthermore, insulation is also required to safely vary the output. Therefore, in order to systemize this circuit by using it in a microcomputer, etc., insulation,
A control device with high pressure resistance is required, and it is no longer suitable for a compact system.

OBJECTS OF THE INVENTION The present invention overcomes the problems of the above-mentioned conventional examples, has a simple circuit configuration, can be systemized, and is intended for all purposes of power control for relatively light loads.

Structure of the Invention In order to achieve the above object, the present invention has the following structure.

That is, from the cross-phase AC lighting, one end is connected to the AC input of the diode bridge through a load and the other end is directly connected to the AC input of the diode bridge, and the drain and source of the power MO8FET are connected to the DC output of the diode bridge. A series circuit of a fixed resistor and a variable resistor is connected in parallel to the drain and source, and the connection point of the fixed resistor and the variable resistor is connected to the gate of the power AV108 FET, and the connection point of the variable resistor is connected to the gate of the power AV108 FET. The structure is such that the voltage applied to the load is varied by varying the resistance value, the load is an induction motor, and the power MO8FETi is attached to the casing of the induction motor.

DESCRIPTION OF THE EMBODIMENTS In FIG. 4, the voltage between the drain and source of the FET 12 is marked 6, which is the difference between the power supply voltage V and the load voltage VL.
.

A voltage obtained by dividing the drain voltage by a fixed resistor 9 and a variable resistor 10 is applied between the gate and the source (hereinafter abbreviated as gate voltage vGs). 6 and 7 are characteristic diagrams of the FET 12. FIG. 6 shows the ID5-■G8 characteristics. Usually, a FET has a threshold voltage vTH,
When the gate voltage vGs exceeds the threshold voltage THk, it enters the ON region and current IDs flows.

FIG. 7 shows more 5-vDs characteristics. Gate voltage vG
The relationship between the drain current IDS and the drain voltage Ds can be seen as the Sk parameter. The dashed-dotted line in Figure 7 is
4 shows the operating points of the circuit shown in FIG. 4. pH-1
:vL-■ indicates the peak current value of s from the drain current when working. vDP indicates the peak voltage value of the drain voltage vDs when ■L-0, that is, ■Ds#■I.When the gate voltage ■Gs value is increased, the s current increases more than the drain current, and the drain voltage ■Ds decreases. The operating point moves to

Furthermore, since the power supply voltage I is an alternating current voltage, the operating point line indicated by the dashed line moves in the direction of the arrow in FIG. 7 due to the phase of the voltage 7.

Therefore, when the value of the variable resistor 10 shown in FIG. 4 is set to a certain value, the operating point A is set at one point on the operating point line connecting IDP-DP'1m. Depending on the phase of the power supply voltage I, the operating point moves on a substantially straight line connecting the operating point A and the origins of s and vvs.

FIG. 5 shows the relationship between the power supply voltage ■I and the load voltage ■L.

Due to the influence of the gate threshold voltage TH described above, in the phase where the voltage value of the power supply voltage I becomes low, the load voltage vL decreases because s is much smaller than the drain current.

However, since the gate threshold voltage vTH decreases relatively slowly with respect to the drain current, there are few harmonic components.

If a FET 12 whose gate threshold voltage is approximately ○ is used, the load voltage (L) can be made almost similar to the power supply voltage (I).

Firebox pressure control is generally used as a means of variable speed for induction motors. As a means of achieving this, there is a stepwise control method for the ratio of the main coil and auxiliary coil of an induction motor, but for air conditioners, this poses a problem of noise and the generation of electrical sound that resonates with the air conditioner's wind tunnel, and is used in some fields. It is not used for anything else.

Since the primary voltage control according to the present invention is a method of varying the voltage applied to the induction motor, the power for the voltage drop is
Since the power FET causes zero heat loss, a heat radiation design using a heat radiator is required.

Regarding the primary voltage control of an induction motor, the efficiency seen from the power source is approximately the same when using ``tap switching control'' and when using a variable voltage method such as the present invention.

Tsu-! The sum of the inputs of the induction motor having a switching tap and the electronic AC voltage variable device of the present invention and the induction motor not having a switching tap are approximately equal in each speed range.

In other words, in the low speed sound range of the induction motor, the loss of the induction motor itself is reduced compared to the tap switching method, and the power FET absorbs the loss.

On the other hand, in the case of tap switching control, the number of taps is normally limited to 3 to 4 due to volume constraints of the induction motor, but according to the present invention, an infinite number of stages can be set. . In addition, the switching means for tap switching control normally uses relay contacts, but there are restrictions on the switching timing and number of switchings due to the life of the contacts and the generation of switching noise. Since it is silent, it is possible to change gears without any restrictions.

Next, the structure will be explained using FIG. 8.

Reference numeral 13 denotes an induction motor having a metal housing used as the load 4, and an FET 12 is attached to the housing for heat radiation. As mentioned above, Jl! : Since the overall efficiency of the induction motor 13, which reduces the loss of TI2, is almost equal to the efficiency of a tap-switching type induction motor, there is no need to modify the induction motor 13 by 10 BEF to dissipate heat from the FET 12.

Effects of the Invention According to the present invention, power control for relatively light loads can be provided compactly and inexpensively, and systemization can be easily achieved.

The first feature is that the power control element can be realized with one element.

Second, the voltage applied to the part that controls the output, ie, the variable resistor 10 in FIG. 4, is low.

This voltage is the gate voltage vGs, so normally 10
It can be controlled with an upper limit of about V. Therefore, AC power supply 10
The control voltage is extremely low for controlling a 0V or 2ooV system, and it can be easily combined with a microcomputer or the like to form a system using a photocoupler or the like.

Furthermore, the circuit configuration is extremely simple and can be constructed at low cost, and even in the event of an abnormality such as a short circuit or open circuit of each component, the load is placed on the power supply side of the circuit, so it has the advantage of being highly safe. There are 11 pebs.

In addition, when controlling the induction motor for the blower of an air conditioner, for example, the air flow rate can be controlled virtually steplessly, and since there are no kidneys or contacts, there are no restrictions on switching operations, and the efficiency of induction motors can be achieved. It does not need to be dropped, and since it uses the casing of the induction motor as a load, a heat radiator can be omitted, and it has many advantages such as improving the feeling, saving energy, and reducing costs.

As described above, it has various excellent effects, and is the most suitable means for systematically controlling voltage of relatively light loads.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional example using slideac, Figure 2 is a circuit diagram showing a conventional example using transistors, and Figure 3 is a circuit diagram showing a conventional example using a transistor.
The figures are voltage control waveform diagrams of Figures 1 and 2, Figure 4 is a circuit diagram of an electronic AC voltage variable device according to an embodiment of the present invention, Figure 6 is a voltage control waveform diagram thereof, and Figure 6 is a circuit diagram of an electronic AC voltage variable device according to an embodiment of the present invention. More than FET 5-
vGS characteristic diagram, FIG. 7 is a s-■Ds characteristic diagram of the FET, and FIG. 8 is a perspective view of the main part thereof. 1...AC power supply, 4...Load, 9...
...Fixed resistor, 1o...Variable resistor, 1
1...Diode bridge, 12...
Power MO8FET', 13...Induction motor. Name of agent: Patent attorney Toshio Nakao and one other person
Peak - Figure 4, Figure 5, Page 6, Figure 7

Claims (1)

[Claims] One end of the AC input of the diode bridge is connected to the load via the
The other end of the trench is directly connected to the phase AC power supply, respectively, and the power MO8FE is connected to the DC output of the diode bridge.
The drain and source of T are connected, a series circuit of a fixed resistor and a variable resistor is connected in parallel to the drain and source, and the power MO3 is connected to the connection point of the fixed resistor and the variable resistor. - The configuration is such that the voltage applied to the load is varied by connecting the gate If of the FET and varying the resistance value of the variable resistor, and the load is an induction motor, and the case of the induction motor is An electronic AC voltage variable device equipped with the power MO8FET.